Page:Physical Geography of the Sea and its Meteorology.djvu/371

Rh east trade-winds is 1,235,250 millions of tons. This is the super-incumbent weight or pressure which is urging the south-east trade-winds forward faster than the north-east. It is inconceivably great; and to bring it within comprehensible terms, the mariner will be astonished to hear that the weight of atmosphere which is bearing down upon the deck of a first-class clipper ship is 15 or 20 tons greater when he is sailing in her through the south-east than it is when he is sailing in her through the north-east trade-winds.

644. Why the barometer should stand higher in the south-east than in the north-east trade-winds.—The question now suggests itself. Why-should the barometer stand higher in the south-east than it does in the north-east trade-winds? The theory of a crossing at the calm belts affords the answer. The air which the north-east trade-winds deliver into the calm belt is not as heavily laden with moisture as that of the south-east trades. It is not as heavily laden for two reasons; one is, the south-east trade-wind belt is broader than the north-east; consequently, in the former there is more air in contact with the evaporating surface. In the